1. Field of the Invention
This invention relates to apparatus for reproducing a helical scan recording by a rotary head. More particularly, this invention relates to such an apparatus for reproducing data signals recorded on plural sectors within plural segments of a single field.
2. Description of the Prior Art
In a helical scan type digital video tape recorder for recording and reproducing NTSC composite signals, a SMPTE D-2 format is employed in which each field is divided into three segments and each segment is recorded on two helical tracks. FIG. 1 shows the D-2 format on a magnetic tape (TP). In this D-2 format, the data of one segment are recorded on two, tracks with each track (T.sub.N) having an azimuth angle different from that of the adjacent tracks. Video data are recorded at the center of each track (T.sub.N). Audio data are recorded at both ends of each track (T.sub.N). The 4-channel audio data (A.sub.0), (A.sub.1), (A.sub.2) and (A.sub.3) are recorded respectively in the four sectors (SC.sub.0), (SC.sub.1), (SC.sub.2) and (SC.sub.3), sectors (SC.sub.0) and (SC.sub.1) are provided at one end of each track (T.sub.N), while sectors (SC.sub.2) and (SC.sub.3) are provided at the other end of each track. The audio data are recorded in duplicate on the sectors at opposite ends of two adjacent tracks. For example, a track (T.sub.0) and a track (T.sub.1) have the same audio data. Referring to FIG. 2, a sector format typical of each sector is shown in which the audio data is formed by six blocks. Each block is composed of a sync (SYNC) pattern, an ID pattern and inner code blocks composed of digital audio data and the check bytes. The ID pattern includes the segment (S.sub.n) and sector sequence information. In order to reproduce the data of D-2format, a rotary magnetic head device (100) is employed. As shown on FIG. 3, the rotary magnetic head device (100) has two pairs of heads (H.sub.A) and (H.sub.B), and (H.sub.C) and (H.sub.D) mounted so that each head of a pair is close to adjacent tracks on the tape (TP). Each of heads (H.sub.A), (H.sub.B), (H.sub.C) and (H.sub.D) is arranged on 180.degree. opposite on a cylindrical rotary drum (DR) in 180.degree. opposition to another of the heads, thereby enabling a pair of heads always to abut the tape (TP).
When shuttle reproduction is performed on such D-2 format, the running speed of the tape (TP) is increased. As shown in FIG. 4, a locus of the head then crosses a plurality of tracks (T.sub.N). Data of the shuttle reproduction mode are corrected to minimize the deterioration in the playback image by using the present digital technique.
In a digital video tape recorder adapted for reproducing the data recorded in the above described D-2 format, data of different tracks are mixed at the time of shuttle reproduction and audio data are reproduced in a state devoid of continuity. Since the data of the different tracks differ in the correction code blocks and hence cannot be corrected, the amount forming the data of audio signals is diminished drastically at the time of shuttle reproduction. As a result, the audio signals cannot be reproduced satisfactorily.